JPH03226511A - Dephosphorizing method of high-manganese molten iron - Google Patents

Abstract

PURPOSE:To suppress the oxidation loss of Mn in a molten iron in dephosphorization by bringing an Na2CO3-SiO2 flux compounded with an Mn oxide into contact with the high-Mn molten iron. CONSTITUTION:The flux essentially consisting of the Na2CO3, SiO2 and Mn oxide is brought into contact with the molten iron contg. >=5wt.% Mn at the time of dephosphorizing this molten iron. If the Mn oxide is MnO2, the amt. of the oxide to be compounded is preferably specified to about 10 to 25 pts.wt. per 10 pts.wt. total of the Na2O in the Na2CO3 compounded with the flux and the SiO2 added with the oxidation forming amt. of the Si with the compd. The flux is preferably so used that the ratio (Na2CO3)/(SiO2) of the Na2CO3 and SiO2 in the slag attains 1.25 to 1.5. The high-Mn molten iron is efficiently dephosphorized at a low cost in this way.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention uses an inexpensive dephosphorizing agent to dephosphorize high-manganese molten iron with a manganese content (Mn) of 5% by weight or more, and
) relates to a method for efficiently dephosphorizing while suppressing oxidation loss.

(Conventional technology) In recent years, as the fields of use of steel materials have diversified, many new steel types have been developed, but the manganese content is approximately 5% (
(Hereinafter, unless otherwise specified, "%" means "weight %") or higher manganese steel is one of them.

High manganese steel as a non-magnetic steel is a competitive material, Ni.
It is not only cheaper than austenitic stainless steel containing austenitic stainless steel, but also has the advantages of high strength and low magnetic permeability. Applications are expanding as non-magnetic steel, structural steel, and wear-resistant steel for nuclear fusion device parts, demagnetization device parts, electrical equipment parts, etc.

By the way, since phosphorus in high manganese steel is generally a harmful substance that adversely affects hot workability and weld cracking resistance, it is desirable to reduce it as much as possible. If cheap ferromanganese is used as a Mn source in melting high manganese steel, the P contained in it will be transferred to the molten iron, increasing the P content CP) of the molten iron. Therefore, it has been customary to add ferromanganese as Mnfi to the extent permitted by the (P) standard, and supplement the remaining Mn with metallic manganese to prevent (P) from becoming too high.

However, this method uses a large amount of expensive metal manganese, resulting in high melting costs.

Therefore, as a lower cost melting technology, most of the Mn
It is essential to establish a technology for producing low-phosphorus, high-manganese molten iron from high-manganese molten iron with a high phosphorus content by blending ferromanganese with ferromanganese.

In response to such demands, several dephosphorization methods for high-manganese molten iron have been developed, but none have been put into practical use.

For example, even the reduced membrane phosphorus method using CaC-CaFz system flux, which is relatively inexpensive, is difficult to put into practical use for the following reasons.

(2) In this reduced membrane phosphorization method, (Ca) is produced by a decomposition reaction as shown in equation 11, and this is dephosphorized by combining with [P] in the molten iron as shown in equation (2).

(CaCz) → (Ca) + 2 (C) −
--(])3 (Ca) + 2 (P) → (Ca
3Pz) -1--12) Here, in order to promote the decomposition reaction shown in formula (1), the lower the amount of (C) in the molten iron, the more advantageous it is, so a prior decarburization treatment is essential.

■In order to prevent air oxidation loss of [Ca), reduced membrane phosphorus must be performed in a non-oxidizing atmosphere, and the dephosphorization efficiency is easily affected by the atmosphere.

(2) After the dephosphorization treatment, the slag easily reacts with moisture in the atmosphere as shown in equation (3), generating harmful phosphine (pHs).

(Ca:+Pz) + 38J →3 (Cab) +
2 PHs ---- (3) On the other hand, the oxide film phosphorization method, which is carried out as a dephosphorization method for ordinary carbon steel and low alloy steel, is used to remove 0□ using CaO-based slag during converter blowing. Even if strong oxidation refining such as blowing is applied as a dephosphorization method for high-manganese molten iron, only (Mn) is preferentially oxidized and (P) in the molten iron cannot be removed.

However, JP-A-61-272312, JP-A-62-30810, JP-A-62-227063,
As proposed in the publication, (P) in the molten iron is oxidized as shown in equation (4) with a weak oxidizing power that does not excessively oxidize (Mn), and then as shown in equation (5). The acidic oxide P20. which is a dephosphorizing component. (P) in the molten iron can be removed by stabilizing it in the slag with BaO, which is a basic oxide that is significantly stronger than CaO in the converter slag.

2 (Pl +5 (0) = (Pies) −
−・(4)(P20s) + 3 (Bad) = (
3BaO・PzOs) '-'-(5) This dephosphorization method using BaO-based slag is easy to process, and there is no problem with slag after dephosphorization, but BaO-based slag is very expensive, so dephosphorization is difficult. The cost is high and it is difficult to adopt it for mass processing.

Furthermore, as an oxide film phosphorization method for high manganese molten iron, "Tetsu to Hagane" 74th year (198B) No. 9 P, 177B describes Na
as+on (sodium orthosilicate), NaaSiOa
A dephosphorization method using NaFz flux using NazO-based slag is introduced.

Although a very high dephosphorization rate can be obtained by the dephosphorization method using this Na*0-based flux, ■Na4SiO is expensive. ■White smoke is generated during the dephosphorization process.

■There is a lot of oxidation loss of (Mn) in molten iron (14%Mn-5%
There is a (Mn) loss of 0.9 to 1.6% in Ci pig iron)
For these reasons, this method is also difficult to put into practical use.

In order to solve the above-mentioned problems with the conventional dephosphorization method for high manganese molten iron, the applicant has proposed using Na, C, which are inexpensive and easily available.
Developed a method for dephosphorizing high manganese molten iron using a flux whose main components are O, and 5ift.
The application was filed as No. 06136.

In the method for dephosphorizing high manganese molten iron of the prior invention, Na
, CO3 and 5ift are used as main components. The main components Na, CO, decompose under high temperature as shown in equation (6).

(NazCOs) → (NazO) 10Cot
----(61 The strong basic oxide Na2O produced is an acidic oxide Pz produced by the oxidation of (P) in molten iron.
Dephosphorization is achieved because Os (the reaction of formula (4) above) is fixed in the slag as shown in formula (7) below.

(Pies) +3 (Na2O)-(3NazO-P
, Os) ""' (7) A part of the CO□ generated at the same time can be used to act as an oxidizing agent for (P) and generate MnO by the reaction shown in equation (8).

C(h + (Mn) -Co 10 (MnO) -(
8) Another main component, 5iOz, is blended in an appropriate amount in order to retain NazO, which evaporates at high temperatures, in the slag at high temperatures. Nano and SiO2 are (Nan
o) It is thought that x.SiO□ (X≧l) is formed, a part of which dissociates and participates in the dephosphorization reaction according to equation (7).

As described above, according to the method for dephosphorizing high-manganese molten iron previously proposed by the present applicant, low-phosphorous, high-manganese molten iron can be produced even if a large amount of cheap phosphorus-containing ferromanganese is blended.

However, when CP) in high-manganese molten iron is formed into an oxide film by the above-mentioned reactions, (Mn) in the molten iron is oxidized at the same time according to equation (8). Since this will reduce the Mn yield of molten iron, measures to prevent this are required. That is, if the oxidation loss of Mn can be suppressed when dephosphorizing by the method of the prior invention, high manganese molten iron can be produced at a significantly lower cost.

(Problems to be Solved by the Invention) The object of the present invention is to provide a method for dephosphorizing high-manganese molten iron using a flux containing Na, CG, and 5ift as main components, and which is a method for dephosphorizing high-manganese molten iron. The object of the present invention is to provide a method for dephosphorizing high-manganese molten iron with little oxidation loss.

(Means for solving !li!) The present inventor has discovered that when dephosphorizing high-manganese molten iron using a Na-COs-SiO□-based flux, Mll in the molten iron is
Various methods of suppressing oxidation loss were investigated.

As a result, it was found that when an appropriate amount of manganese oxide is added to Na=COs-5iOg-based Franks, the dephosphorization rate slightly decreases, but the oxidation loss of Mn in molten iron can be significantly reduced, and this greatly increases the dephosphorization effect. It was confirmed that this is an extremely practical method to reduce the manufacturing cost of high manganese steel without inhibiting the production of high manganese steel.

The present invention is a method for dephosphorizing high-manganese molten iron using 'NazCOs 5iO1-based flux, in which a flux containing manganese oxide as well as NazCOs and SiO2, which are the main ingredients, is used with a manganese content of 5% by weight.
A method for dephosphorizing high-manganese molten iron characterized by bringing it into contact with the molten iron described above.''

In this method, manganese oxide is mixed in advance into the Na=COs-3iOz flux, so that the (Mn) in the molten iron (hereinafter, the components in the hot metal are indicated by the symbol [ ], and the components in the slag are indicated by the symbols ()). When the manganese oxide is Mn01, the amount of the manganese oxide is the same as that of Na=COs in the flux.
For a total of 100 parts by weight of 2O and SiO2, which is the addition of the amount of oxidized (Si) produced in the flux, 10 to
It is desirable that the amount is 25 parts by weight.

The manganese oxide to be blended is other than MnO*, for example, Mn.
It may also be O2MnxOs, Mn5O4, etc.

In addition, in this dephosphorization method, (N
Dephosphorization is performed by generating a slag mainly composed of a2O)
It is desirable to use a flux such that (SiO8) is 1.25 to 1.5, (NazO)/(Sto
w) is Na in Na2CO3 mixed in flux,
This is the ratio between 0 minutes and the sum of SiO2 mixed in the flux and SiO2 produced by oxidation of (Si) in the molten iron.

The amount of other O1 produced by oxidation of (S2) in the molten iron can be calculated assuming that (Si) is substantially all SiO2, so it can be calculated from the [S2] content of the molten iron to be treated. can be easily found.

(Function) Figures 1, 2, and 3 show the results of basic tests (crucible experiments) in developing the method of the present invention. The test was conducted under the following conditions.

(a) Treated molten iron: (Mn)'=13%, (C) t4%, (P) #0.06
% of molten iron, treatment temperature = 1300''C (b) Flux used: Na=COs 5ift Mn0t flux, however, since molten iron does not substantially contain (Si), here the property formation during dephosphorization is considered. There is no need to consider 5ift, so the flux is (NazO)/(
SiOz) is approximately 1.25, CNaxCO: 95 kg) + (SiOt: 45
The ratio of b), i.e. (Nano: 55 kg) + (
Shot: 45kg) = 100kg ratio Te1
latCO* and SiJ were blended, and 20 kg of MnO* was also blended to prevent Mn oxidation loss.

Figure 1 shows [P] and (
MFl) and (MnO) and (NazO) in the slag
/(SiO□). [P] used to be 0.060%, but it decreased to 0.0 after 30 minutes of processing.
The dephosphorization rate has decreased to 18%, and the dephosphorization rate reaches 70%.

Approximately 0.5% of [Mn] in molten iron is oxidized during treatment, and the reason for this is due to the excess C in the Na, CO, and Na added as shown in equation (6) above. It is presumed that Mn is oxidized as shown in equation (8), and that (Mn) is oxidized as shown in equation (9) below due to the oxidizing power of NazO itself.

Na, O+Mn-+ MnO+ 2 Na
-49) Therefore, (MnO) in the slag after dephosphorization
The flA degree increased from 20% to nearly 30%. (M
If the oxidation loss of n) proceeds through the reactions of formulas (8) and (9), Mn01MnO
It is thought that the oxidation loss of (Mn) can be suppressed if a manganese oxide such as x is mixed in advance. Furthermore, since Nano evaporates during the treatment, (NazO)/(SiJ) decreases over time from the pre-treatment noflux of 1.25.

Figure 2 shows the dephosphorization rate, (
This figure shows the results of examining Mn) oxidation loss and (MnO) concentration after treatment.

As shown in FIG. 2, by incorporating MnO□ into the flux, the oxidation loss of (Mn) is reduced.

However, when the blending amount of Mn0z exceeds 25 kg/T, the oxidation loss of (Mn) increases. This is thought to be due to the fact that the oxidizing power of the slag becomes too large and oxidizes (Mn).

The general phosphorus rate increases as the Mn0t content increases, and the
nO) gradually decreases as 4 degrees increases. This is ■
This is because the (NaJ) concentration in the slag decreases due to dilution accompanying the addition of MnO, and (2) Since MnO is a weaker basic oxide than Na and O, the basicity of the slag as a whole becomes weaker.

Therefore, we can obtain the same dephosphorization rate (65 to 70% or more under the present experimental conditions) as in the case without the addition of MnO, and reduce the oxidation loss of (Mn) to 1 in the case without the addition of MnOz.
．． 3%, to suppress it to 0.5% or less, Naz
C(1+5iOz flux(D((Mail
) + (Sift) MnO for 1100kg/T
It is desirable that the blending ratio of 2 is 10 to 25 kg/T.

Figure 3 shows the dephosphorization rate and (Mn) oxidation loss by changing the flux (Na2O)/(SiOt) (other conditions are the same as in Figure 1, but treatment time is 30 minutes). The results of the investigation are shown in comparison with cases in which Mn0t is added and cases in which Mn0t is not added.

As shown in the figure, when manganese oxide is blended into the flux (solid curve in No. 3 UjJ), the dephosphorization rate is slightly lower than when it is not blended, but the amount of oxidation loss of (Mn) is reduced by about 0.5 Can be reduced by ~1.5%* (NazO)/(SiOz) with or without Mn01 blended
≧1.0, the dephosphorization reaction progresses, and (NazO)/(Si
As the value of O□) increases, the dephosphorization rate increases logarithmically, and the amount of oxidation loss of (Mn) increases exponentially.

(NazO)/(Sift) < 1.25 (M
Although the amount of oxidation loss in n) is suppressed to a low level, the dephosphorization rate is significantly reduced.

When (NaxO)/(Sift) is in the range of 1.5 to 2.0, the dephosphorization rate improves slightly and reaches the upper limit, whereas the amount of oxidation loss of Mn) increases rapidly, but there is no Mn0t in the flux. By blending, the amount of oxidation loss is reduced to approximately 0.5
It can be lowered by ~1.5%. From the practical point of view of suppressing the oxidation loss amount of (Mn) to the lower limit without significantly inhibiting the dephosphorization rate, the flux should be 1.25≦(
Na, CO to satisfy the condition of Na2O)/(SiO2)≦1.5.

It is desirable to have a mixture of 5ift and 5ift. However, as described above, if Si is contained in the molten iron before treatment, (SiO2) is the total amount of the blended amount in the flux and the amount of SiO□ produced by oxidation in the molten iron (S2).

Next, the conditions for the molten iron components will be described.

The higher the content of (C) in molten iron, the more desirable it is for dephosphorization.

This is due to the following two reasons. One of them is that the higher (C) is, the lower the melting point of molten iron is, so dephosphorization can be performed at a lower temperature. Since the oxide film phosphorization reaction is generally an exothermic reaction, the lower the temperature, the more advantageous it is for dephosphorization. Another reason is that when (C) is high, P
The thermodynamic concentration (activity) of molten iron increases, which is advantageous for dephosphorization.

However, in the sense that no burden is placed on the decarburization process that is a post-dephosphorization process, there is an upper limit to (C) in actual operation. If we take these points together, 2%≦(C)≦4%
can be said to be a desirable range.

(Si) in molten iron causes an increase in slag deposition and a decrease in slag basicity in the case of oxidized phosphorus caused by CaO-based or BaO-based basic slag, so it is important to limit the upper limit of (S2). is common. However, in the method of the present invention, there is no strict limit on the upper limit of (Si).
This is also one of the major features of the method of the present invention. In other words, since the method of the present invention uses NatCOs as a Nano source, CO8 produced during the treatment causes (S
2) is oxidized, 5iQ1 is deposited on the slag layer, and is removed to form a dephosphorizing slag as (Nano), 5iOt (x≧1). Therefore, if the (Si) content in the molten iron is high, it can be dealt with by reducing the amount of 340g to be mixed, and it is not necessary to carry out the usual preliminary desiliconization treatment of the molten iron.For example, (N
Using 100 kg of a flux of 0) + (SiOz) per ton of molten iron, (Na2O)/(SiOz
) = 1.5, (S2)
can be tolerated up to a maximum of 1.8%.

When high-manganese molten iron is dephosphorized using NaxCOz 5ins flux, the effect of (Mn) in the molten iron on the dephosphorization rate and the amount of (Mn) oxidation loss is shown in Figure 4. Previous Mn concentration in molten iron (
Mn) =1. is 18% compared to 13%.
The value of the achieved dephosphorization rate is about 5-30% lower, and (Mn)
The amount of oxidation loss was approximately the same at this level of (Mn) = □.

According to the method of the present invention, (Mn) oxidation loss is further suppressed by incorporating manganese oxide into the flux, so that the upper limit value of the dephosphorization rate can be obtained from the value of (NazO)/(SiO□). , 5~2.0 and NazCO2-Si
O2-based flux may also be used.

Next, the dephosphorization treatment temperature will be described.

The dephosphorization treatment temperature is determined based on the thermodynamic reasons mentioned above, and
The lower the temperature, the better because it suppresses the evaporation of Nano and reduces the erosion of the refractory.

For example, it is better to be 50 to 100 degrees Celsius higher than the melting point of molten iron.
In actual operation, the temperature of the molten iron before the dephosphorization treatment is desirably set at a temperature 150 to 450° C. higher than the melting point, depending on the capacity of the furnace, taking into consideration the temperature drop due to flux addition.

Next, the amount of flux added will be described.

The required amount of flux to be added is based on the initial [P] of the molten iron to be treated.
) and the desired dephosphorization rate, but the required amount may be selected within the range of approximately 20 kg to 120 kg per ton of molten iron.

The flux used can be in the form of solid particles or powder, and the addition method can be either the overlay method or the injection method into molten iron, but the injection method of powdered flux is most effective. Dephosphorization progresses.

It is better to mix Na, CO, and SiO□ that make up the flux before adding them. This is because the reaction can be carried out quickly and the evaporation of the Na2O component can be minimized. It is also a good idea to mix the powder of manganese oxide with the flux in advance.

The apparatus for carrying out the method of this invention is A.
Examples include OD furnaces and other furnaces in which stirring gas can be introduced from the bottom of the furnace. It is also possible to perform the treatment by bubbling agitation using Ar gas or the like in a ladle or by impeller agitation.

(Example) Three types of high manganese molten iron having the compositions shown in Table 1 (before treatment) were each melted in the atmosphere in a 10 ton electric furnace, poured into an AOD furnace, and then heated to the same (predetermined temperature shown in Table 1). It was adjusted.

Then, add the flux shown in Table 2 onto the molten iron, and
Dephosphorization treatment was performed while stirring with r gas for about 10 minutes. In the comparative example, the flux shown in Table 2 without Mn0t was used.

The chemical composition after treatment is also listed in Table 1. Note that the (NaxO)/(SiO2) values in Table 2 are based on (SiO2) values during processing.
) is oxidized to produce 0 g of Si.

As is clear from Table 1, (Mn) i++i is approximately 1
In Example 1 and Comparative Example 1 at the 1% level, the dephosphorization rates were 76% and 79%, respectively, and the ('Mn) oxidation loss amounts were 0.5% and 1.2%, respectively.

Example 2 and Comparative Example 2 with (Mn) rat about 20%
The dephosphorization rates are 64% and 67%, respectively, (Mn)
The amount of oxidation loss was 1.5% and 2.4%, respectively.

(Mn)=. In Example 3 and Comparative Example 3, in which , was about 24%, the dephosphorization rates were 60% and 65%, respectively, and the [Mn) oxidation loss amounts were 1.8% and 3.6%, respectively.

From the above results, by implementing the method of the present invention,
Without significantly inhibiting dephosphorization of high manganese molten iron
It is clear that the amount of [Mn] oxidation loss can be reduced.

Table 2 (SjOz) shows the blending amount in Franks and the content in molten iron (Si
shows the total weight including the amount of oxidation produced from;

(Hereinafter, blank space) (Effects of the invention) According to the method of the present invention, NaxCOi-
By incorporating manganese oxide into 5iO□-based Franks, it is possible to efficiently dephosphorize high-manganese molten iron while suppressing the amount of oxidation loss of Mn in molten iron. It is extremely useful for manufacturing high-manganese steel at low cost.

[Brief explanation of drawings]

Figures 1, 2 and 3 show Na=C0=Si
Figure 1 shows the results of a dephosphorization experiment of high manganese molten iron using Ot-MnO□ system Franks. Figure 2 shows the relationship between the amount of MnO added, the dephosphorization rate, the amount of (Mn) oxidation loss, and the (MnO) in the slag. , (Maze)/(Sift) and the dephosphorization rate and (Mn) oxidation loss amount. Figure 4 shows the results of a dephosphorization experiment of high manganese molten iron using NazCOs SiO□ system Franks.
azO)/(SiOt) value, dephosphorization rate and (Mn)
The relationship with the amount of oxidation loss (Mn) i*i is 13% and 18
It is a figure which compares and shows the case of %.

Claims (3)

[Claims] (1) Na_
A method for dephosphorizing high manganese molten iron, characterized by contacting a flux containing 2CO_3, SiO_2 and manganese oxide as main components. (2) Na in Na_2CO_3 mixed in flux
A claim characterized in that a flux containing 10 to 25 parts by weight of MnO_2 is used with respect to 100 parts by weight of the total amount of SiO_2 mixed in the flux, SiO_2 mixed in the flux, and SiO_2 generated by oxidation of Si in the molten iron. The method for dephosphorizing high manganese molten iron according to item (1). (3) Na in Na_2CO_3 mixed in flux
The ratio of the _2O content to the total amount of SiO_2 blended in the flux and SiO_2 generated by oxidation of Si in the molten iron, that is, (Na_2O)/(SiO_2) is 1.
The method for dephosphorizing high manganese molten iron according to claim 1 or 2, characterized in that the blending ratio of the flux is determined to be 25 to 1.5.